1. Field of the Invention
The present invention relates to improvements in and relating to a power-assisted hand carrier such as a motorized wheelbarrow.
2. Description of the Related Art
One example of known power-assisted hand carriers is disclosed in Japanese Patent Laid-open Publication HEI 3-265403. The disclosed power-assisted hand carrier includes a geared motor for rotating wheels of the hand carrier via a differential unit, and a single handlebar operatively connected with the geared motor for controlling operation of the geared motor. The handlebar is designed to move back and forth in response to a force applied thereto from the operator so that power generated by the geared motor varies with the amount of displacement of the handlebar.
It is proved that the conventional power-assisted hand carrier operates satisfactorily when used in a relatively wide working area or moving over relatively smooth ground surfaces. However, when the conventional power-assisted hand carrier is used in a relatively narrow working space or moving over rough or angulated ground surfaces, the force applied to the handlebar changes frequently with the result that assist power generated by the geared motor changes frequently, too. To deal with this frequent changes of assist power, the operator is forced to frequently change its working posture. Thus, the operator is subjected to a heavy burden or working load. This problem becomes significant when the hand carrier is to be moved backward because the operator should pay attention to the presence of an obstacle right behind the hand carrier.
It is accordingly an object of the present invention to provide a power-assisted hand carrier which is easy to handle and can exhibit good mobility when used in a relatively narrow working area or moving over rough or angulated ground surfaces.
To attain the forgoing object, there is provided, according to the present invention, a power-assisted hand carrier which comprises: a body frame; a load-carrying platform supported by an upper portion of the body frame; a pair of left and right handlebars extending from a rear portion of the body frame obliquely upward in a rearward direction of said body carrier; and at least one wheel rotatably supported by said body frame. A power unit is mounted on the body frame for producing rotating power. The power unit is operatively connected with the wheel such that the wheel is driven in rotation by the rotational power. A controller is provided for controlling operation of said power unit to change the direction and intensity of the rotating power so that the wheel can be driven in both forward and backward directions at a variable speed.
In one preferred form, the hand carrier is a power-assisted wheelbarrow having a single wheel which is supported by the body frame at a transverse central portion of the wheelbarrow.
The controller preferably includes a manually operated forward drive control member provided on a distal end portion of one of the handlebars for enabling the power unit to operate in such a manner as to produce necessary power assist for moving the hand carrier in a forward direction, and a manually operated reverse drive control member provided on the distal end portion of the one handlebar for enabling the power unit to operate in such a manner as to produce power for driving the hand carrier in a backward direction.
It is preferable that the manually operated forward drive control member is a slidable grip slidably mounted on the distal end portion of the one handlebar and movable in the forward direction in response to a forward thrust applied to the slidable grip, and the manually operated reverse drive control member is a manually operated reverse drive control lever pivotally mounted on the one handlebar in the proximity of the slidable grip. The controller further includes a first displacement sensor mounted on one of said one handlebar and the body frame for detecting a forward displacement of the slidable grip and producing an output signal corresponding to the detected forward displacement of the slidable grip, and a second displacement sensor mounted on one of said one handlebar and the body frame for detecting an angular displacement of the manually operated reverse drive control lever and producing an output signal corresponding to the detected angular displacement of the manually operated reverse drive control lever. The power unit produces the power assist based on the output signal from the first displacement sensor and also produces the driving power based on the output signal from the second displacement sensor.
The first displacement sensor may be a linear reciprocating potentiometer mounted on the one handlebar in the proximity of the slidable grip and having a slide rod directly connected to the slidable grip for reciprocating movement in unison with the slidable grip.
Preferably, the second displacement sensor is a potentiometer having a built-in selector switch for selecting one of the output signal from the first displacement sensor and the output signal from the second displacement sensor for the control of operation of the power unit. The selector switch is normally disposed in a position such that the output signal from the first displacement sensor is selected.
The potentiometer of the second displacement sensor may be a rotary potentiometer mounted on the body frame and having a rotary shaft operatively connected to the manually operated reverse drive control lever to rotate in response to pivotal movement of the manually operated reverse drive control lever, or a linear reciprocating potentiometer mounted on the one handlebar and having a slide rod operatively connected to the manually operated reverse drive control lever to reciprocate in response to pivotal movement of the manually operated reverse drive control lever.
Preferably, the power unit includes a drive source for producing rotational power, and a power transmitting mechanism for transmitting the rotational power from the drive source to the single wheel. The power transmitting mechanism includes a forward-reverse changeover clutch disposed in the proximity of an axle of the single wheel for mechanically switching rotating direction of the single wheel between the forward direction and the reverse direction.
In one preferred form, the forward-reverse changeover clutch includes: a forward drive bevel gear and a reverse driven bevel gear rotatably mounted in face to face on the axle; a drive bevel gear rotatably driven by the drive source and being in mesh with the forward and reverse driven bevel gears; forward clutch teeth forward on a surface of the forward driven bevel gear facing the reverse driven bevel gear; reverse clutch teeth formed on a surface of the reverse driven bevel gear facing the forward driven bevel gear; a clutch pin movably received in a longitudinal intermediate portion of the axle such that the clutch pin is movable along the axis of the axle with its opposite end portions projecting from the axle in a radial outward direction; a resilient member urging the clutch pin toward one end of the axle; the axle having an axial blind hole coaxial with the axle and extending from the one end toward the other end of the axle; a shift rod slidably fitted in the blind hole and having an inner end held in abutment with an outer peripheral surface of the clutch pin by the action of the resilient member, the shift rod being adapted to be manually reciprocated to move the opposite end portions of the clutch pin selectively into meshing engagement with the forward clutch teeth or the reverse clutch teeth.
Preferably, the axle has a radial guide slot extending radially through the longitudinal intermediate portion of the axle and slidably receiving the clutch pin, and a spacer collar is disposed between the surfaces of the forward and reverse driven bevel gears and extends around the longitudinal intermediate portion of the axle to prevent removal of the clutch pin from the radial guide slot.